1. Field of the Invention
The present invention relates to Toll-Like Receptor 5 (TLR5). In particular, the invention relates to antisense oligonucleotides that specifically hybridize with nucleic acids encoding TLR5, thus modulating TLR5 expression and activity, and their use in treating or preventing diseases associated with TLR5 or wherein modulation of TLR5 expression would be beneficial.
2. Summary of the Related Art
Toll-like receptors (TLRs) are present on many cells of the immune system and have been shown to be involved in the innate immune response (Hornung, V. et al., (2002) J. Immunol. 168:4531-4537). TLRs are a key means by which mammals recognize and mount an immune response to foreign molecules and also provide a means by which the innate and adaptive immune responses are linked (Akira, S. et al. (2001) Nature Immunol. 2:675-680; Medzhitov, R. (2001) Nature Rev. Immunol. 1:135-145). In vertebrates, this family consists of at least 11 proteins called TLR1 to TLR11, which are known to recognize pathogen associated molecular patterns (PAMP) from bacteria, fungi, parasites and viruses and induce an immune response mediated by a number of transcription factors.
Some TLRs are located on the cell surface to detect and initiate a response to extracellular pathogens and other TLRs are located inside the cell to detect and initiate a response to intracellular pathogens. Table 1 provides a representation of TLRs, the known agonists therefore and the cell types known to contain the TLR (Diebold, S. S. et al. (2004) Science 303:1529-1531; Liew, F. et al. (2005) Nature 5:446-458; Hemmi H et al. (2002) Nat Immunol 3:196-200; Jurk M et al., (2002) Nat Immunol 3:499; Lee J et al. (2003) Proc. Natl. Acad. Sci. USA 100:6646-6651); (Alexopoulou, L. (2001) Nature 413:732-738).
TABLE 1Cell TypesTLR MoleculeAgonistContaining ReceptorCell Surface TLRs:TLR2bacterial lipopeptidesMonocytes/macrophagesMyeloid dendritic cellsMast cellsTLR4gram negative bacteriaMonocytes/macrophagesMyeloid dendritic cellsMast cellsIntestinal epitheliumTLR5motile bacteriaMonocyte/macrophagesDendritic cellsIntestinal epitheliumTLR6gram positive bacteriaMonocytes/macrophagesMast cellsB lymphocytesEndosomal TLRs:TLR3double stranded RNADendritic cellsvirusesB lymphocytesTLR7single stranded RNAMonocytes/macrophagesviruses;Plasmacytoid dendritic cellsRNA-immunoglobulinB lymphocytescomplexesTLR8single stranded RNAMonocytes/macrophagesviruses;Dendritic cellsRNA-immunoglobulinMast cellscomplexesTLR9DNA containingMonocytes/macrophagesunmethylatedPlasmacytoid dendritic cells“CpG” motifs; DNA-B lymphocytesimmunoglobulincomplexes
The signal transduction pathway mediated by the interaction between a ligand and a TLR is shared among most members of the TLR family and involves a toll/IL-1 receptor (TIR domain), the myeloid differentiation marker 88 (MyD88), IL-1R-associated kinase (IRAK), interferon regulating factor (IRF), TNF-receptor-associated factor (TRAF), TGFβ-activated kinasel, IκB kinases, IκB, and NF-κB (see for example: Akira, S. (2003) J. Biol. Chem. 278:38105 and Geller at al. (2008) Curr. Drug Dev. Tech. 5:29-38). More specifically, for TLRs 1, 2, 4, 5, 6, 7, 8, 9 and 11, this signaling cascade begins with a PAMP ligand interacting with and activating the membrane-bound TLR, which exists as a homo-dimer in the endosomal membrane or the cell surface. Following activation, the receptor undergoes a conformational change to allow recruitment of the TIR domain containing protein MyD88, which is an adapter protein that is common to all TLR signaling pathways except TLR3. MyD88 recruits IRAK4, which phosphorylates and activates IRAK1. The activated IRAK1 binds with TRAF6, which catalyzes the addition of polyubiquitin onto TRAF6. The addition of ubiquitin activates the TAK/TAB complex, which in turn phosphorylates IRFs, resulting in NF-κB release and transport to the nucleus. NF-κB in the nucleus induces the expression of proinflammatory genes (see for example, Trinchieri and Sher (2007) Nat. Rev. Immunol. 7:179-190).
The selective localization of TLRs and the signaling generated therefrom, provides some insight into their role in the immune response. The immune response involves both an innate and an adaptive response based upon the subset of cells involved in the response. For example, the T helper (Th) cells involved in classical cell-mediated functions such as delayed-type hypersensitivity and activation of cytotoxic T lymphocytes (CTLs) are Th1 cells. This response is the body's innate response to antigen (e.g. viral infections, intracellular pathogens, and tumor cells), and results in a secretion of IFN-gamma and a concomitant activation of CTLs. TLR5 is known to localize on the cell membrane and is activated by flagellin, which is a principal component of bacterial flagella and serves as a virulence factor recognized by the innate immune system in plants, insects, and mammals (Hyashi et al. (2001) Nature 410:1099-1103). This ability of TLR5 to respond to flagellin demonstrates TLR5's ability to generate an immune respond to a broad group of motile pathogens.
As a result of their involvement in regulating an inflammatory response, TLRs have been shown to play a role in the pathogenesis of many diseases, including autoimmunity, infectious disease and inflammation (Papadimitraki et al. (2007) J. Autoimmun. 29: 310-318; Sun et al. (2007) Inflam. Allergy Drug Targets 6:223-235; Diebold (2008) Adv. Drug Deliv. Rev. 60:813-823; Cook, D. N. et al. (2004) Nature Immunol. 5:975-979; Tse and Horner (2008) Semin. Immunopathol. 30:53-62; Tobias & Curtiss (2008) Semin. Immunopathol. 30:23-27; Ropert et al. (2008) Semin. Immunopathol. 30:41-51; Lee et al. (2008) Semin. Immunopathol. 30:3-9; Gao et al. (2008) Semin. Immunopathol. 30:29-40; Vijay-Kumar et al. (2008) Semin. Immunopathol. 30:11-21). While activation of TLRs is involved in mounting an immune response, an uncontrolled or undesired stimulation of the immune system through TLRs may exacerbate certain diseases in immune compromised subjects or may cause unwanted immune stimulation. Thus, down-regulating TLR expression and/or activity may provide a useful means for disease intervention.
To date, investigative strategies aimed selectively at inhibiting TLR activity have involved small molecules (WO/2005/007672), antibodies (see for example: Duffy, K. et al. (2007) Cell Immunol. 248:103-114), catalytic RNAi technologies (e.g. small inhibitory RNAs), certain antisense molecules (Caricilli et al. (2008) J. Endocrinology 199:399), and competitive inhibition with modified or methylated oligonucleotides (see for example: Kandimalla et al. US2008/0089883; Banat and Coffman (2008) Immunol. Rev. 223:271-283). For example, chloroquine and hydroxychloroquine have been shown to block endosomal-TLR signaling by down-regulating the maturation of endosomes (Krieg, A. M. (2002) Annu Rev. Immunol. 20:709). Also, Huang et al. have shown the use of TLR4 siRNA to reverse the tumor-mediated suppression of T cell proliferation and natural killer cell activity (Huang et al. (2005) Cancer Res. 65:5009-5014), and the use of TLR9 siRNA to prevent bacterial-induced inflammation of the eye (Huang et al. (2005) Invest. Opthal. Vis. Sci. 46:4209-4216).
Additionally, several groups have used synthetic oligodeoxynucleotides having two triplet sequences, a proximal “CCT” triplet and a distal “GGG” triplet, a poly “G” (e.g. “GGGG” or “GGG”) or “GC” sequences that interact with certain intracellular proteins, resulting in the inhibition of TLR signaling and the concomitant production and release of pro-inflammatory cytokines (see for example: Lenert, P. et al. (2003) DNA Cell Biol. 22(10):621-631; Patole, P. et al. (2005) J. Am. Soc. Nephrol. 16:3273-3280), Gursel, I., et al. (J. Immunol., 171: 1393-1400 (2003), Shirota, H., et al., J. Immunol., 173: 5002-5007 (2004), Chen, Y., et al., Gene Ther. 8: 1024-1032 (2001); Stunz, L. L., Eur. J. Immunol. (200) 32: 1212-1222; Kandimalla et al. WO2007/7047396). However, oligonucleotides containing guanosine strings have been shown to form tetraplex structures, act as aptamers and inhibit thrombin activity (Bock L C et al., Nature, 355:564-6, 1992; Padmanabhan, K et al., J Biol. Chem., 268(24):17651-4, 1993). Thus, the utility of these inhibitory oligodeoxynucleotide molecules may not be achievable in patients.
A potential approach to inhibiting, suppressing or down regulating expression of TLRs is antisense technology. The history of developing antisense technology indicates that while designing and testing antisense oligonucleotides that hybridize to target RNA is a relatively straight forward exercise, only a few antisense oligonucleotides work as intended and optimization of antisense oligonucleotides that have true potential as clinical candidates is not predictable. One skilled in the art would recognize that when optimizing antisense oligonucleotides, conceiving the correct oligonucleotide sequence and length, and utilizing the appropriate nucleic acid and oligonucleotide chemistries are not readily apparent. However, formulating these components is crucial to the utility of any antisense oligonucleotide (Stein and Cheng, 1993, Science 261: 1004-1012). One skilled in the art would further recognize that without conceiving the correct sequence, the correct length, and utilizing the appropriate nucleic acid and oligonucleotide chemistries, the antisense oligonucleotide can have off-target effects and can cause, among other things, the molecule to be unstable, inactive, non-specific, and toxic. As a result of the unpredictable nature of antisense oligonucleotides, to date only one antisense oligonucleotide has received approval for use in humans, and no antisense oligonucleotides are currently being marketed for human use.
Accordingly, there exists a need in the field for optimized antisense oligonucleotides that most efficiently down-regulate or inhibit gene expression. In particular, there exists a need in the field for antisense oligonucleotides that down-regulate TLR5 expression and that are stable, active, target specific, non-toxic, and do not activate an innate immune response. A molecule with such characteristics would overcome the problems that have previously prevented antisense oligonucleotides from being developed.